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2007+part+c+answers - akPlCOlSC more AnswUS owe asmidas...

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Unformatted text preview: akPlCOlSC more: AnswUS owe, asmidas poserbla. lilo” Wt” new +0 show 41:1: WOVKWS and smre any OlSSUmPhODS “you have madc)0+he,vwnsa mavks will be deducted. PART C Short answer question, Total 50 marks RECORD ANSWERS ON THIS EXAM PAPER . Question I (8 marks) (a) Diethyl ether, used as a solvent for extraction of organic compounds from aqueous solutions, has a high vapor pressure which makes it a potential fire hazard in laboratories in ' which it is used. How much energy is released when 100.0 g is cooled from 530°C to 100°C? - boiling point 345°C heat of vaporization 351 J/g Specific heat capacity, (CH3)2O(I) 3.74 J/(g-K) specific heat capacity, (CH3)2O(g) 2.35 J/(g-K) Fmou ems/weir =-4—%-(o a?) (4 marks) (b) Carbon tetrachloride, once widely used in fire extinguishers and as a dry cleaning fluid, has been found to cause liver damage to those exposed to its vapors over long periods of time. What is the boiling point of a solution prepared by dissolving 375 g of sulfur (83, M = 256.5 g/mol) in 1250 g of CCl4? Kb = 5.050C/m, boiling point of pure COL}: 767°C Bounds pom-r :. 826°C (4 marks) CHM104 200740 , Page 13 of 20 Question 2 (9 marks) (a) Write hydrolysis reactions for the following salts and state whether they are acidic, basic or neutral. (i) potassium carbonate K“’(aq) 4— H200“) No reachon— {a erplmetalg 0032’s. + H o a Hcoi" + OH C q) 2 .(il 3(0‘51) (QC!) (2 marks) (ii) aluminium chloride A103 LS) —9 Al5+(qq) + 30' #039) MSW”) t szoooai [A‘(”zolb]5+(°'Q) 2+ + [tang-125%]5+ + 1420(1) -—> [A1 (H10)50Hj(aq) + H50 (qu Cilaq)+ H2000 % NO Vgccifl$bbose OF”??? )QC/id (b) What is the plél for a buffer that consists of 0.20 M NaH2PO4 and 0.40 M Nazi-IP04? Ka = 6.2 x 10' pH= "7-51 (3 marks) (0) Explain the direction and relative extent (slight or significant) of pH change, if 0.5mL of 0.1M HCl was added to the buffer described in Question 2(h). Extent 01° pH Chumse, {s shat/1+ due +0 bu-PFU' e-FFaor . CHMIM 200740 ' Page 14 of 20 Question 3 (10 marks) (a) He C: Describe the bonding in ethylene (ethene, C2H4) according to valence bond theory. Draw a diagram clearly showing at least one bond of each type which occurs in the molecule. H H C/ / \ H) do Uble bond 6 b H cwc Smalé’. bond 03) (C) (d) (2 marks) Draw Lewis structure(s) for $03 which obey the octet rule, showing all valence electrons. /\ " "- ’\ /\ ’\ O 70/ \0 0' O 0 \\// \ // S. a \‘s/ «a s. [9 i ' llg‘ \O/ (2 marks) Draw the Lewis structure of XeF4. Use this structure, in conjunction with VSEPR theory, to predict (and name) the shape of this molecule. Outline your reasoning. X} \EL Squat/C Plat/TOU/ (3 marks) In a single atom, write down the maximum possible number of electrons that may be described as follows. Show workings () W‘thn=3 1 1 q OVIOK'I’OJS \SUQQtvoms (1 marks) (ii). with the designation 4d 5 ovmrals match/om (1 Marks) (iii). with n = 5,1: 3, ms = + 1/2 ‘l OVbl‘i'OtlS low only 1 89‘?ch 7 elem/ens CHMIU4 200740 Page 15 of 20 H Slam? at 1. Question 4 (4 marks) (a) What is the frequency of microwave radiation which has a wavelength of 10.7 cm? j : 280 x qu 5’! (2 marks) (b) What is the energy of one photon of this radiation? E — l-8b x :0'24‘J .’ . (2 marks) Question 5 (11 marks) (a) At a certain temperature the reaction C02(g)+H2(g) ‘75 C0(g)+H20(g) has Kc = 1.20 X 103. If 2.00 mol of carbon dioxide and 1.5 mol of hydrogen are placed in a 5.00 L vessel and equilibrium is established, what will be the concentration of carbon monoxide? Make any reasonable assumption, clearly stating what that assumption is. [co] -.= o-OSM (5 marks) CHMIW 200740 Page 16 of 20 Question 5 continued 0?) The following reaction is at equilibrium in a closed container: 2Fe(OH)3(s) —> Fe203(s) + H20(g) (AH° > 0) What effects, if any, will the following actions have on the position of equilibrium? In each case, state the direction of any shift in equilibrium, and give your reasons in one sentence. (i) adding more Fe(OH)3 No 2,4396% (2 marks) (ii) raising the temperature i Rea (mom a (2 k (iii) adding acatalyst mar 5) N o 6F? w- (2 marks) CHM104 200 740 ' Page 17 of 20 Questior: 6 (8 marks) Lead (11) bromide, Pbez, is an ionic compound with a solubility product constant K31, of2.1 x 10‘6. Calculate the solubility of this compound in: a. pure water 8 8-07 x lo'sM (4 marks) 1). 0.50 mol L'1 PbNO3 solution 8 1-02x10‘3M ll (4 marks) CHMIDtI 200740 Page 18 of 20 ...
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